US Patent 10345521 Method of modifying mode size of an optical beam, using a waveguide mode expander having non-crystalline silicon features

A waveguide mode expander couples a smaller optical mode in a semiconductor waveguide to a larger optical mode in an optical fiber. The waveguide mode expander comprises a shoulder and a ridge. In some embodiments, the ridge of the waveguide mode expander has a plurality of stages, the plurality of stages having different widths at a given cross section.